Expression of Gα(z) in C2C12 cells restrains myogenic differentiation.

The recent identification of Gα(z) expression in C2C12 myoblasts and its demonstrated interaction with the transcription factor Eya2 inferred an unanticipated role of Gα(z) in muscle development. In the present study, endogenous Gα(z) mRNA and protein expressions in C2C12 cells increased upon commencement of myogenesis and peaked at around 4-6days after induction but were undetectable in adult skeletal muscle. Surprisingly, stable expression of recombinant Gα(z) in C2C12 myoblasts strongly suppressed myotube formation upon serum deprivation, and the constitutively active mutant Gα(z)QL exerted more pronounced effects. Transcriptional activities of reporter genes responsive to early (MyoD, MEF2 and myogenin) and late (muscle creatine kinase and myosin heavy chain) myogenic markers were reduced by transiently expressed Gα(z)QL. Membrane attachment of Gα(z) was apparently required for the suppressive effects because a fatty acylation-deficient Gα(z) mutant could not inhibit myogenin expression. Introduction of siRNA against Gα(z) enhanced myogenin-driven luciferase activity and increased myosin heavy chain expression. Immunostaining of C2C12 cells over-expressing Gα(z) showed delayed nuclear expression of myogenin and severe myotube deformation. Gα(z) expression was accompanied by reduced levels of Rock2, RhoA and RhoGAP, enhanced expression of Rnd3, and a reduction of serum-responsive factor-driven reporter activity. These results support a novel role of Gα(z) in restraining myogenic differentiation through the disruption of Rho signaling.

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